WASHINGTON—President Donald Trump on Friday pardoned a former top aide to Vice President Dick Cheney who was convicted in 2007 of lying to a grand jury and obstructing justice in a case that culminated in the leaking of a CIA officer’s identity.

I. Lewis “Scooter” Libby, now 67 years old, was sentenced to 30 months in prison. Then-President George W. Bush commuted that sentence, describing it as “excessive,” but he didn’t issue a pardon, despite entreaties from Mr. Cheney. Mr. Libby’s conviction capped a four-year investigation...